1. Field of the Invention
This invention relates generally to building materials. More specifically, the invention relates to a lightweight panel construction that is suitable as a substitute or alternative for conventional gypsum wallboard.
2. Prior Art
The interior framing of residential and commercial buildings is typically covered or finished with sheets of gypsum board, commonly referred to as drywall, wallboard or Sheetrock(copyright) (trademark of U.S. Gypsum Company). Conventional gypsum wallboard has a gypsum plaster core faced with sheets of paper, and normally is made in standard size panels with dimensions of 4xc3x978, 4xc3x9712 or 4xc3x9716 feet, and thicknesses ranging from xe2x85x9c inch up to xc2xe inch, although thicknesses as little as xc2xc inch can be obtained by special order for specialized use.
Considerable transportation costs, and difficulty in handling and installation are associated with conventional gypsum wallboard because of its density and weight. Moreover, gypsum wallboard is susceptible to moisture damage, and is easily dented or broken if struck near the edges or corners. Further, relatively expensive landfill costs are associated with disposal of conventional gypsum board.
Alternatives to conventional gypsum wallboard have been proposed, including wood particle board, and lightweight materials such as paper fiber, composites of synthetic materials, and/or honeycomb reinforcing structures faced with various materials, including plaster or conventional sheets of gypsum board.
U.S. Pat. No. 3,106,503, for example, discloses a composite wallboard having a paper honeycomb core which can be faced on one or both sides with commercially available conventional sheets of gypsum board. The principal object of this patent is to provide a structural panel that can withstand direct contact with flame, and which may be moisture resistant. Further, a stated object is also to provide a lightweight structural panel that has superior qualities of rigidity and strength. However, commercially available sheets of gypsum board having conventional thickness, i.e., from xe2x85x9c inch up to xc2xe inch, are applied to the honeycomb core. The panels described in this patent are therefore relatively heavy and hard to handle in that they still incorporate sheets of gypsum board having conventional thickness, and the composite panel appears to have a total thickness substantially greater than the thickness of conventional gypsum board. Further, manufacture of the panels described in this patent is relatively complicated and expensive.
U.S. Pat. No. 3,170,827 discloses a method of making an insulation panel having facing sheets of asbestos cement board separated by approximately six inches of polyurethane foam reinforced with honeycomb paper. In making the panel, a layer of foam-forming chemicals is deposited on a bottom facing sheet, a honeycomb structure is pressed into the chemical layer into bonding relationship with the bottom facing sheet, the foam is expanded, and a top facing sheet is placed on top of the structure, in contact with the expanded foam, which bonds the components together.
U.S. Pat. No. 3,246,058 discloses a method for producing reinforced foam laminate structures, wherein a reinforcement member, e.g., corrugated material, is fed between two continuously supplied spaced sheets of facing material, at least one of which has been coated with an organic foam material, and the foam is expanded to fill the space and bond the components together.
U.S Pat. No. 3,249,659 discloses a method of making structural panels useful as walls, partitions, doors, truck bodies and the like, wherein a core is interposed between facing sheets and partially filled with a foamed plastic to form an air space therein. In particular, a layer of foam-forming mixture is applied to the inner surfaces of the facing sheets, a reinforcing member is inserted between the sheets, and the layers of foam-forming mixture are expanded toward one another but without merging. A structure analogous to an I-beam is thus formed.
U.S. Pat. No. 4,351,870 discloses a panel construction especially suitable for earthquake and fire resistance, and adapted for assembly of pre-fabricated components to form a building. The panel includes one or more layers of strength-increasing material separated by lower strength bulk-producing layers which may comprise foamed plastic or foam rubber materials. Facing sheets such as wood veneer, plastic simulated wood veneer, wallpaper finish, brick, tile, or plaster may be used to obtain a desired appearance.
U.S. Pat. No. 4,917,742 discloses a method of making lightweight building panels having a foam-filled honeycomb core faced with fiberglass-reinforced plastic sheets.
U.S. Pat. No. 5,309,690 discloses a lightweight composite panel intended as a substitute for gypsum board. The panel comprises a cellular core filled with an inorganic insulating material and a material which releases water at elevated temperatures, and first and second sheets such as corrugated cardboard bonded to opposite sides of the core.
U.S. Pat. No. 5,338,594 discloses a lightweight insulation and structural material for building and aerospace industries, wherein a honeycomb structure is filled with a polycyanurate foam. The foam is expanded in the honeycomb cells while contained by pressure plates above and below the cells.
U.S. Pat. No. 5,679,433 discloses a non-combustible wall decorating panel having a honeycomb core and a metal foil facing sheet.
Although the prior art discloses a variety of panels, some of which have good strength-to-weight ratios, including panels suitable for use in the building industry, it does not disclose any lightweight and tough panel intended as a substitute for conventional gypsum board wall panels, wherein the substitute panel has the same surface characteristics as conventional gypsum board panels, i.e., it has a surface veneer of paper-covered gypsum plaster, and preferably has the same dimensional relationships, whereby the panel may be installed and finished using conventional techniques and equipment.
Accordingly, there is need for a panel that has the same surface characteristics as a conventional gypsum board, and has the same dimensional relationships, but is substantially lighter in weight while at the same time possessing superior toughness.
The invention is a composite panel for use in place of conventional gypsum board panels, and that has the same surface characteristics and preferably the same dimensional relationships as a conventional gypsum board panel, but is significantly lighter in weight while at the same time possessing superior toughness.
The panel of the invention is an improvement over conventional drywall or gypsum board primarily because of its greatly reduced density, which results in a weight reduction of sixty or percent or greater, and the benefits associated with this reduced density. These benefits include reduced transportation costs and requirements, reduced labor for handling and installation, less dust and debris when working with the panel, improved workability and elimination or reduction of landfill fees required for disposal, and potentially a reduction of structural members that would otherwise be required in a building simply to support the considerable weight of conventional gypsum board.
The panel of the invention comprises an open cell reinforcing core structure faced with a thin gypsum board veneer, and has a greatly improved strength-to-weight ratio compared with conventional gypsum board panels, especially when it employs a foam-filled core construction, being synergistically stronger than either the open cell core structure or the gypsum board alone.
One open cell core construction suitable for use in the invention is the Hexacombtm packaging material made by Pactive Corporation (formerly Tenneco). This packaging material is a paper honeycomb structure, and in one embodiment comprises strips of 33 lb. liner glued together at contact lines running in the machine direction. Each strip of core paper is aligned such that the machine direction is in the thickness direction of the core. The primary fibers are thus aligned with the machine direction, resulting in the greatest compression strength and stiffness.
A gypsum board facing sheet or veneer is applied to at least one side of the core, to provide the same surface characteristics and appearance as conventional gypsum board. This facing sheet is only deep or thick enough to obtain these characteristics, i.e., to enable normal working of the panel, namely, sanding, cutting, finishing and acceptance of fasteners, in the same way as obtained with conventional sheets of gypsum board. A suitable thickness for the gypsum facing sheet or veneer would be in the range of from about {fraction (1/16)} of an inch up to about xe2x85x9 of an inch, or even up to xc2xc of an inch.
For example, to produce a panel having a standard nominal thickness of xc2xd inch, a facing sheet of xe2x85x9 inch thickness could be applied to a honeycomb core having a thickness of xe2x85x9c inch; or, a facing sheet of {fraction (1/16)} inch thickness could be applied to a honeycomb core having a thickness of {fraction (7/16)} of an inch; etcetera. Similarly, to produce a panel having a xc2xe inch thickness, the facing sheet could be only xe2x85x9 inch thick, but the core thickness would be increased to ⅝ inch; or alternatively, a thinner facing sheet, e.g., {fraction (1/16)} inch, could be applied to a core having a thickness of {fraction (11/16)} of an inch. It should be understood that the gypsum facing sheet could have other thicknesses, as long as it is thick enough to impart the desired surface characteristics to the panel, but not so thick as to unnecessarily increase the weight of the panel. Thickness of from about {fraction (1/16)} of an inch up to about xc2xc inch, for example, may be suitable.
A panel constructed in accordance with the invention is stronger near the edges and corners than a conventional gypsum board, because the foam-filled core material does not break and crumble near the edges as will conventional gypsum board. It is also anticipated that the installation or addition of electronic circuitry will be easier than with conventional gypsum board. For instance, circuitry can be embedded in the cells of the core, in the facing, or between the cells and facing, which can facilitate construction of the xe2x80x9chouse of the futurexe2x80x9d. For example, sensors which can track the location of specific objects or persons, monitor and control climate settings, record events, etc., can be incorporated into the structure. Moreover, portions of the core may be left open to provide raceways or channels for utilities or the like.
The core material can be paper-based or other material such as plastic or a composite. If paper-based, the core material can be bleached or unbleached, virgin or recycled, or a combination thereof, and can be impregnated or coated with a suitable resin or other material selected for its desired properties. The core construction can be either honeycomb, corrugated, or laminations of corrugated layers or combinations of corrugated and honeycomb. If a honeycomb core construction is used, the cell size can typically vary from xe2x85x9c inch to 1 inch center-to-center, although other dimensions can be employed. The foam used to fill the core can be a fire rated or fire retardant foam, or a foam having other desirable properties, and can be selected from any of those commercially available, for example.